The therapeutic potential of peptide drugs has remained unfulfilled due to the unfavorable physicochemical properties of these molecules. Peptides are extremely susceptible to proteolytic degradation in blood and tissues. The hydrophilic nature of peptides severely limits their permeability across hydrophobic cell membranes. 2) RC-160, a potent somatostatin analog is one of the most extensively studied therapeutic peptides for its anti-proliferative and anti-secretory activity.

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... rp-Lys-Val-Cys-Trp-NH 2 The anti-proliferative activity of the somatostatin analog RC-160 is limited by its short serum half life. To circumvent this limitation, fatty acids of chain lengths ranging from 4 to18 were individually conjugated to the N-terminal residue of RC-160. The lipophilized derivatives of RC-160 were synthesized, purified and characterized. The anti-proliferative activity of lipophilized-RC-160 on the human breast carcinoma cell line MCF-7, was evaluated in vitro. The long chain lipopeptides like pamitoyl-RC-160 exhibited significantly higher anti-proliferative activity on MCF-7 cells (pϽ0.001), relative to RC-160. The affinity of RC-160 towards somatostatin receptors remained unaltered by pamitoylation. However, the observed increase in bioactivity was manifested within an optimum range of chain length of thelipoppetide. Increasing the peptide hydrophobicity beyond this range reduced the bioactivity of lipophilized-RC-160. Accordingly, stearoyl-RC-160, manifested lower anti-neoplastic activity and receptor affinity relative to pamitoyl-RC-160 and RC-160 itself. The signaling pathways underlying the antineoplastic activity of these lipopeptides were found to be similar to RC-160. Pamitoyl-RC-160 displayed enhanced inhibition of protein tyrosine kinase activity and intracellular cAMP levels in MCF-7 cells, relative to butanoyl-RC-160 or RC-160 itself. Pamitoyl-RC-160 also displayed greater resistance towards trypsin and serum degradation than RC-160. Lipophilization of RC-160 with long chain fatty acids like pamitic acid improves its stability and anti-proliferative activity, thereby improving the scope of enhancing its therapeutic index. However, the optimization of peptide hydrophobicity seems to be a crucial factor governing the efficacy of bioactive lipopeptides.